Total joint replacement, a surgical procedure wherein a damaged joint is removed and replaced with a new prosthetic joint, has become increasingly common due to a growing need for joint replacement and to improvements in artificial joint technology, arthroplasty surgical techniques, and postoperative treatment regimens. It has been estimated that in the U.S. alone, approximately one million hip or knee total joint replacement surgeries are performed annually. The Agency for Healthcare Research and Quality reported that more than 600,000 total knee replacements are performed each year in the United States.
Arthritis is the most common cause of chronic knee pain and disability. A 2010 study by the Center for Disease Control and Prevention reports that 50 million U.S. adults had arthritis in 2007-2009, an increase of about 9% from 2003-2005. Osteoarthritis, rheumatoid arthritis, and post-traumatic arthritis are the most prevalent forms of arthritis, resulting in chronic knee pain. Non-surgical treatments, such as anti-inflammatory medications, cortisone injections, lubricating injections, physical therapy, and the like, are typically undertaken to improve joint function and to diminish pain. If non-surgical treatments are not successful, total joint replacement may be indicated.
In a typical knee joint replacement procedure, the femur and tibia are first prepared by removing the damaged cartilage surfaces along with a small amount of bone. Metal implants are then cemented to the ends of the femur and tibia. Optionally, the patella may be resurfaced. Then a spacer, generally a medical-grade plastic spacer, is inserted between the metal components.
Total knee replacements have been called one of the most successful procedures in medicine, with upwards of 90% of patients having total knee replacement surgery reporting significant reduction of knee pain and improvements in ability to perform normal daily tasks. The complication rate following total knee replacement surgery is low. Serious complications such as knee joint infection occur at rates that have been reported in the range of 1% and 3%.
Although an infected prosthetic knee is sometimes removed and replaced with a new prosthesis in a single operation, greater success at curing the infection has been achieved using a two-stage surgical procedure. In the first stage the infected prosthesis is removed and replaced with a temporary, antibiotic-infused cement spacer which is left in vivo between the femur and the tibia, typically for several weeks. The classic way a cement spacer has been made is to combine bone cement powder, antibiotics, and a monomer to form a doughy cement that is placed into the knee space and allowed to harden with the leg extended, and then closing the wound. The antibiotic in the spacer leaches out over time to treat the infection. More recent spacers or temporary joints provide additional support structure. The temporary spacer may be a static spacer or may be articulated, to allow flexure of the knee joint. In the second stage the temporary spacer is removed, and a permanent total knee prosthesis is implanted. An example of a first stage spacer is disclosed in U.S. Pat. No. 8,097,039, to Evans, the disclosure of which is hereby incorporated by reference.
One problem with conventional static spacers is that the antibiotic cement placed into the defect formed by the removal of the artificial knee may not provide sufficient stability to the joint. Even though the joint is not intended to move, voluntary or involuntary muscle contractions can cause motion in the joint, which may be painful and could damage the fragile bone further. One way to support the joint is to install an intra-medullary rod extending between the tibia and femur, and cementing it with bone glue so that the bones cannot move. However, it may be difficult to place the intra-medullary rod between the two bones, as the procedure requires first sliding the intra-medullary rod far up into the medullary cavity of one bone, and then repositioning (extending) the joint and moving the rod back into the medullary cavity of the other bone, such that the rod is disposed in both medullary cavities and spans the gap therebetween. This procedure may contaminate the medullary cavity further, and carry bone glue further into the bone than is desired. It can also be very difficult to remove the rod.
There remains a need for improvements to first stage spacers or temporary joint replacements that are more easily installed, provide improved joint stability, provide antibiotic treatment deep into the tissue, and are adjustable to accommodate particular patients and procedures.